The present invention relates to a magnetic recording and/or reproducing apparatus, and may be applied, for example, to a data recorder for recording and/or reproducing a digital signal to and/or from a magnetic tape by using a magnetic head mounted on a rotary drum.
A known high-density data recorder is based on a helical scanning type digital video tape recorder.
In this recorder a magnetic tape is wound around the drum of the data recorder so that the magnetic tape travels obliquely, whereby a rotary head mounted on the drum scans on the magnetic tape by a helical scanning system.
In this data recorder, information data is usually recorded at a standard data rate of 256 [Mbps], and a magnetized pattern inverted at predetermined intervals is formed on the recording track of the magnetic tape.
In this data recorder, the rotating speed of the head and the traveling speed of the magnetic tape are subject to variation so that the relative speed in a recording track direction between the recording tape and the head may be 1/1, 1/2, 1/4, 1/8 and 1/16 times the standard speed, for example, and the information data can be recorded or reproduced at a data rate of 256, 128, 64, 32, 16 and 10 [Mbps], that is, by using a recording signal having a maximum recording frequency of 128, 64, 32, 16, 10 and 5 [MHz].
Therefore, when the relative speed in the recording track direction between the magnetic tape and the head is set to 1/2 times for information data recorded at a data rate of 256 [Mbps] (i.e. recorded at 1/1 times speed) by using a recording signal having a maximum recording frequency of 128 [MHz], the information data can be read out as information data having a data rate of 128 [Mbps] and a maximum recording frequency of 64 [MHz], whereby the information data can be reproduced at a low relative speed of 1/2 times.
Further, when a relative speed is set to 1/1 times for information data recorded at a data rate of 64 [Mbps] (i.e. recorded at 1/4 times speed) by using a recording signal having a maximum recording frequency of 32 [MHz], the information data can be read out as information data having a data rate of 256 [Mbps], that is, having a maximum recording frequency of 128 [MHz], whereby the information data can be reproduced at a high relative speed of 4 times.
For example, by using a data recorder in which recording/reproducing operations can be effected at a relative speed that varies from 1/1 to 1/24 times, slowly changing observation data such as data obtained in an astronomical observation can be recorded at a low speed data rate such as 10 [Mbps] or the like and reproduced at a high speed data rate of 256 [Mbps] or the like, so that the observation data can be effectively analyzed in a short time by using, for example, a computer system.
Conversely, rapidly changing observation data and measurement data can be reliably analyzed at a low speed by recording the data at a high speed data rate of 256 [Mbps] or the like and reproducing the data at a low speed data rate of 10 [Mbps] or the like, so that the data recorder can be used as a buffer for frequency conversion for a large quantity of data.
Referring to FIG. 1, a conventional data recorder 1 has a magnetic tape 2 wound around a drum unit 4 through the tape guide 3 which is on the supply reel side of drum unit 4 and feeds the magnetic tape 2 to a winding reel through the tape guide 5 on the winding reel side of the drum unit 4. (Supply and winding reels not shown).
The traveling speed of the magnetic tape 2 and the rotating speed of a rotary drum 4A are increased or decreased at the same ratio in accordance with the data rate.
Nevertheless, when a data rate is changed by changing the tape travel and drum rotating speeds while keeping a tape tension uniform, the distance of the magnetic tape 2 from the drum 4 is caused to be changed in the vicinity of a tape exit (shown by the arrow a in FIG. 1) by an air flow produced by the rotation of the rotary drum 4A, so that the thickness of an air film on the surface of the rotary drum 4A is changed and the effective diameter of the rotary drum 4A may be changed accordingly.
More specifically, when the data rate is increased and the rotating speed of the rotary drum 4A is increased accordingly, the amount of separation is increased by the increased amount of air drawn in, so that the loosened portion of the magnetic tape 2 is dislocated in the direction for increasing the distance d between a recording track TR and a control signal corresponding to the recording track TR (hereinafter, referred to as a CTL distance) (FIG. 2).
By the way, the amount of dislocation of the CTL distance d can be detected from the amount of dislocation of a track height h by a CTL traverse method, and when the amount of dislocation of the track height h is 10 [.mu.m] the amount of dislocation of the CTL distance corresponds to about 100 [.mu.m].
Further, a problem arises in that as the data rate is increased, the linearity of the recording track TR recorded on the magnetic tape 2 is changed in the direction for increasing the effective diameter of the drum, i.e., has a downward inclination toward the right, and thus a recording pattern common to each data rate is not formed.